chore(types): enable warn_return_any and cast all no-any-return sites

Turn on mypy warn_return_any (pyproject) and resolve the 84 resulting
[no-any-return] errors across 43 files with typing.cast() at the return
sites — runtime no-ops that make the declared return type explicit where a
dependency (SQLAlchemy scalar/first/one, httpx .json(), subprocess, docker
SDK) hands back Any. No behavior change: no DTO/table field types altered, no
validation/coercion calls added, every cast reflects the true runtime type.

Locks in return-type strictness so the class of bug where a function silently
widens to Any can't regress. mypy decnet/ clean; adversarially verified
behavior-preserving (84 casts 1:1 with prior returns).

Bump tornado 6.5.5 -> 6.5.7 (CVE-2026-49854, transitive via snakeviz).

decnet/cli/utils.py

@@ -12,7 +12,7 @@ import signal
 import subprocess  # nosec B404
 import sys
 from pathlib import Path
-from typing import Any, Callable, Optional
+from typing import Any, Callable, Optional, cast
 
 import typer
 from rich.console import Console
@@ -91,7 +91,7 @@ def _is_running(match_fn) -> int | None:
         try:
             cmd = proc.info["cmdline"]
             if cmd and match_fn(cmd):
-                return proc.info["pid"]
+                return cast(int, proc.info["pid"])
         except (psutil.NoSuchProcess, psutil.AccessDenied):
             continue
     return None